Feedback from New Editors
(This is off topic but I am not going to let that stop me.)
I think it entirely depends on what source one obtains via WikiSource - but they have been chosen because someone thought they might be useful. For example, yesterday I made this edit. That's not a very good source, not because it's on de.wikisource or because it dates to 1889, or because it's in German, but because it's another encyclopedia. Secondary sources - for example, academic works on the history of the Cologne archdiocese or on the 15th-century politics of the German states - would be better. But since I started by translating the de.wikipedia article, my next step was to check its references (in this case sources) and use those I can get access to. Today and/or tomorrow I'll look for other works I can cite, with emphasis on non-encyclopedic books and articles. And that isn't a bad source - that particular encyclopedia (and the one I cited with the next 2 edits) are known to be good. As it happens the older one is available on wikisource, while the newer one is online in a pdf or something similar. That's not really the issue in using them - it's their nature as sources that matters.
I think Wikisource is laudable, and very useful for older stuff (for example, de.wikisource also has the text of all editions of Grimm's Fairy Tales, but handicapped by being restricted to sources free of copyright. GoogleBooks gives me access to far more and I don't think Wikipedia either can or should try to beat GoogleBooks at the digitization game. It would be a waste of effort, and with regards to helping editors, it would be analogous to those books that collect together articles on both sides of an issue to make it easier for students to research their first ever research essay. There's always more stuff in the rest of the library, let alone on the internet.